Fix races in snapshot integration test (#146)

This test failed more often than not in my local testing.
Previously we only waited for the pod to be running
which didn't guarantee the file had been created, nor
that it had been sync'ed to the block device.

test/kubernetes/integration_test.go

@@ -358,6 +358,24 @@ func TestSnapshot_Create(t *testing.T) {
 			Name: "my-csi-app-2",
 		},
 		Spec: v1.PodSpec{
+			// Write the data in an InitContainer so that we can guarantee
+			// it's been written before we reach running in the main container.
+			InitContainers: []v1.Container{
+				{
+					Name:  "my-csi",
+					Image: "busybox",
+					VolumeMounts: []v1.VolumeMount{
+						{
+							MountPath: "/data",
+							Name:      volumeName,
+						},
+					},
+					Command: []string{
+						"sh", "-c",
+						"echo testcanary > /data/canary && sync",
+					},
+				},
+			},
 			Containers: []v1.Container{
 				{
 					Name:  "my-csi-app",
@@ -370,7 +388,7 @@ func TestSnapshot_Create(t *testing.T) {
 					},
 					Command: []string{
 						"sh", "-c",
-						"echo testcanary > /data/canary && sleep 1000000",
+						"sleep 1000000",
 					},
 				},
 			},